An object of the present invention is to improve the positioning between a patient and an RF-imaging coil in magnetic resonance imaging apparatus by means of a supporting aid for the coil and the patient. The coils and supporting equipment can be used for producing images of a patient by means of a magnetic resonance imaging apparatus over the head, neck, back and limb portions of a patient.
An object of the invention is to provide an elastic and soft cushion, yielding to the anatomy of a patient and, if necessary, serving as a part of the RF-imaging coil.
The RF-imaging coils of a magnetic resonance imaging apparatus are used both as transmitters and receivers for an RF-signal. In view of maximizing the signal-to-noise ratio, the RF-receiving coils must be designed in their winding dimensions as small as possible, yet in a manner that the picture area achieved thereby covers a desired anatomical object. Therefore, a separate RF-receiving coil is most preferably constructed for each object to be imaged. Typically, these include e.g. head, neck, back, body and knee imaging coils. In order to avoid movement-related artifacts the patient must also remain stationary during an imaging session, which is generally appr. 15 minutes in duration.
An RF-frequency excitation pulse required in imaging is produced by means of an RF-transmitting coil which, in view of achieving a good transmission field homogeneity, is usually a separate coil larger in dimensions than RF-receiving coils. Sometimes both the receiving and transmitting coil can be combined as a single RF-coil.
The direction of an applied DC-magnetic field has a major effect on the winding geometry of coil designs.
In terms of their mechanical construction, the prior known RF-receiving coils are generally hard objects which do not allow for a shape conforming to the anatomy of a particular patient. In the case of such a coil, it is possible to imitate the anatomical shape but, due to the individual variation in anatomy, the coil winding generally tends to stay far away from the object resulting in a poorer picture quality.
It is generally known that the coils of a hard mechanical structure always require some soft object separate from or fastened to the coil to serve as a cushion between patient and coil. If the piece of cushion is not anatomically shaped or designed, it does not necessarily provide a sufficient support for a patient. The cushioning piece can be designed to comply with anatomy, but it is impossible to cover all variations with a single design. Thus, the cushioning pieces may be available in various shapes and sizes, whereby the right one must be found by fitting to the patient. This may prove difficult with barely movable patients. In addition, the fitting efforts may take too much of valuable examination time.
It is known that the use of soft coils adds to the comfort of a patient. If the coil is also flexible, it will also be capable of adjusting to anatomical variations. However, without a support which is sufficient and arranged in view of the individual anatomical shape of a patient it is not possible to sufficiently exploit all the benefits offered by a soft coil.
It is known that the back coils are generally hard or padded flat objects, which are placed under the back and upon which a patient is laid on his/her back. This type of flat structure does not take into consideration the anatomical variation resulting from curvature of the spine. This problem is encountered especially in those coils that are long in the longitudinal direction of the spine, e.g. coils with an elliptical winding or coils consisting of several successive winding elements. What may happen in this situation is that the coil with a good signal-to-noise ratio shall remain too far away from the spine resulting in a poorer picture quality.
In the neck and throat area there is also considerable anatomical variation per individual patient. Generally, the prior known neck and throat coils are hard objects which conform to the anatomic shapes of the target area. Due to the individual differences between patients, however, the inside coil dimensions must be made according to the largest patients, resulting in a poorer picture quality on smaller patients for whom such a coil is too large. The coils can be produced in a plurality of sizes but this increases the price of the apparatus.
In head imaging, the head is conventionally set on a special head rest, which takes care of a proper head position during the course of imaging and whose purpose is also to maintain the head stationary. The head rests are generally trough-like hard objects. Supporting or bracing is generally effected by using separate or head-rest mounted support pieces, which may come in various shapes and sizes and which are generally soft. Positioning and finding the proper pieces takes time and a support suitable for each patient is not necessarily found. Sometimes the head is also braced by using a belt which is tied over the head.